I am a border rat. I’ve been one since the day I hopped back and forth between countries over a fallen, rusty barbed-wire fence in the woodland along the Arizona-Mexico line some 40 years ago. Since that act of joyful anarchy, I’ve traveled the entire length of the frontier numerous times, dined and slept in just about every border town on both sides and chatted with folks of high and low life throughout.

There’s comfort in binational familiarity. Last October, I had encebollada — thin sirloin strips with onion — at the landmark restaurant Mrs. Crosby’s in Ciudad Acuña, Mexico, and across the parking lot I could see the window of the hotel room I’d rented exactly 30 years before.

There are lots of us border rats, really — most from the U.S. side but many from Mexico as well. We share music, food and a language. Some live within a few miles of the line and know it intimately, while others, like me, are chronic visitors. For decades now, I’ve maintained that the entire border is a third country no more than 20 miles wide and about 2,000 miles long. We border rats can navigate this 40,000-square-mile turf far more easily than we could the interior of our own homelands. We know where the tortillas are thinnest, where the music is jazziest, where the cops are friendliest and where the crossings are easiest.

But that was yesterday. Today the United States-Mexico border has been pancaked between a collapsed economy to the north and brutal drug thugs to the south. Most Mexican border towns have endured at least one horrific moment recently in which a ranking police officer or journalist or político of some standing has been murdered or kidnapped in public, often with a number of innocents unfortunate to be near him — almost always a him — as collateral damage. Then there’s that ugly wall scarring our beautiful borderland, whose repulsiveness will surely outlast its short-term effectiveness.

One result of this dreadful situation is that border towns in both countries, but far more so in Mexico, have seen their economies disappear. It used to be common for borderlanders crossing over to shop, dine, visit family and friends (on both sides), see a doctor or pharmacist (the Mexican side) or just soak in a different atmosphere. Now, from Brownsville and Matamoros on the Gulf of Mexico to San Diego and Tijuana on the Pacific coast, shopkeepers on the U.S. side see only a trickle of Mexican customers.

On the Mexican side, matters are far worse. The main boulevards, which used to jump with tourists in the cafes and in shops that sold goods from the interior, are now like streets in a ghost town. Late one afternoon during my visit to Ciudad Acuña (est. pop. 175,000), I was shoeshine man Valencio Ayala’s second customer as he wrapped up his 11-hour workday. Hidalgo Street was deserted save for one elderly American couple poignantly dancing to the sunset sounds of three street musicians.

A State Department travel alert in the fall of 2008 warned of violence along the Mexican border and mentioned Nogales, in the Mexican state of Sonora, by name. One week before Christmas, when Obregón Avenue in this city of about 190,000 is usually packed with shoppers from Arizona, my wife and I took a one-hour walk through town to her dentist and saw barely a handful of Americans along the way.

As if to reinforce what lies south of the border, a U.S. Forest Service sign north of the line cautions visitors: “Smuggling and illegal immigration may be encountered in this area.” (Or, as California author Rubén Martínez paraphrases it, “Don’t feed the Mexicans.”) The U.S. Army has warned soldiers stationed at Fort Hood in Texas and Fort Huachuca in Arizona to stay away from the Mexican border.

Nowhere does the change in border dynamics appear more striking than in Ciudad Juárez, a city of about 1.5 million across the Rio Grande from El Paso. Juárez, which in recent years has seen a string of unsolved sexual assaults and murders of young women, was once the swingin’-est town on the entire frontier. Here, at the crossroads of NAFTA, terrific literature, quality artisan crafts, foreign-owned assembly plants and dance halls galore, the erosion of border life as it existed for generations is almost complete. Juárez awoke one day last December to learn that four policemen had been killed within a half-hour, one of them decapitated. It was the worst carnage of that week, but it numbed rather than outraged. Juárez experienced more than 1,500 homicides last year, which, along with daylight carjackings, occasional kidnappings, random street robberies and plain vanilla extortion, made for a population fearful of the new year.

Lest you think that rampant narco turf wars there are fairly recent, it was more than 10 years ago that Tom Russell, who lives outside El Paso, went to the afternoon bullfights in Juarez with a friend. Afterward, they headed to the nearby Max Fim restaurant, then impulsively decided not to have dinner there after all. Later, they learned that drug thugs had attacked the eatery, killing a rancher and five bystanders. A month later, Russell told a magazine interviewer, he and his friend passed up a post-bullfight meal at another place, Geronimo’s. As their cab pulled away, an automatic weapon began to fire at the restaurant. Six people were killed.

Russell is an acclaimed singer-songwriter, and borderland nostalgia has seldom been as evocatively expressed as it is in his song “When Sinatra Played Juárez.” He sings of Uncle Tommy Gabriel, a Texas border rat who once used to gallivant around Juárez. But now: “He lives out on his pecan farm. ‘I don’t cross the bridge,’ he said, ’cause everything’s gone straight to hell since Sinatra played Juárez.’ ”

Whenever I go to El Paso, I ring up local friends to arrange a foray across the river. A visit to Juárez cafes, a baseball game, a nightclub or an open-air marketplace is always a high point of any El Paso trip. My border rat companions, some of them natives of that metropolitan area, have always been game and have invariably introduced me to yet another locale to add to my list. When I called during a visit last September, though, I heard hemming and hawing. They stay in El Paso, they said; Juárez is no longer on their dance card. These are people whose judgment I trust, and a sad, uncomfortable feeling sank in.

I began to understand Uncle Tommy Gabriel: “I don’t cross the bridge,” he said.